Bottom base of vacuum flask



FIG. 1 is a front elevation view of a bottom base of vacuum flask showing my new design;

FIG. 2 is a rear elevation view thereof;

FIG. 3 is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a first perspective view thereof; and,

FIG. 8 is a second perspective view thereof.

In the drawings, the evenly dashed broken lines showing the remainder of the vacuum flash illustrate features which form no part of the claimed design. 

CLAIM The ornamental design for a bottom base of vacuum flask, as shown and described. 